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Snags and nurse trees


insectivores that provide natural control, preventing insect populations from reaching epidemic proportions.
  • Birds. Many bird species are attracted to snags and represent one of the most significant benefits. Besides insectivorous species that forage on dead trees, many birds live in cavities. Primary cavity-dwelling birds are those that excavate their own nests, including woodpeckers and nuthatches. Hard snags are most suitable for this purpose. These nests may subsequently be occupied by secondary cavity-dwellers such as owls, ducks, chickadees, titmice, wrens and swallows. Soft snags provide additional foraging sites.
  • Mammals. Bats take shelter under the loose bark of snags in early stages of decay. They also nest in cavities, as do squirrels, flying squirrels, fishers and martens.
  • Salamanders. Fallen trees in advances stages of decay provide important habitat.
  • Lichen and fungus.
  • Plants. Many species flourish in the nutrient rich soil provided by nurse trees. In fact tree saplings often gain a foothold on life from the remains of previous generations. In West Coast rainforests, where huge nurse trees may persist for centuries, it is a common to see a giant mature tree rooted on the remnants of another that must have fallen before Europeans arrived in North America. Rainforest soils are relatively thin and poor due to the heavy leaching of precipitation. In these conditions, dead trees provide an essential nutrient reservoir.

    Falling trees also create openings in the forest, called tree-fall gaps. These allow more light to penetrate to the forest floor, stimulating the growth of young saplings and other vegetation. These sites enhance the diversity of plant species in a forest and attract additional wildlife such as deer and small mammals.

    Snags are a common and important feature of rivers through woodland habitat. Trees growing along the banks tend to grow sideways toward the light, making their root systems relatively unstable. Many fall, becoming partly or fully submerged. These snags provide shelter and breeding sites for fish and other species. Turtles use them for sunbathing.

    Snags are not only important in mature forests, but in earlier stages of habitat progression, too. The preferred nest site of bluebird, for example, is tree cavities alongside meadows and fields. The removal of old orchards contributed to the bluebird's decline.

    My first visit to a mature temperate rainforest in 1987 gave me a fresh awareness of nature. Having lived my entire life in Southern Ontario I was unfamiliar with climax forests. The aspect of so much decay bewildered me. Western urban culture, far removed

    The copyright of the article Snags and nurse trees in Ecology is owned by Van Waffle. Permission to republish Snags and nurse trees in print or online must be granted by the author in writing.

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